High voltage sparkplug

ABSTRACT

A high-voltage sparkplug has an electrically conductive housing from one end of which a ground electrode projects. An elongated center electrode extends through the housing and has a first end portion projecting from the one end and defining a spark gap with the ground electrode and a second end portion projecting from the opposite end of the housing and having a free terminal. An electrical insulator insulates the center electrode from the housing and includes an elongated insulator portion which surrounds the second end portion of the center electrode intermediate the housing and the terminal and is provided in its outer circumferential surface with a plurality of axially spaced grooves which serve to retard current leakage between the terminal and the housing by increasing the sparkover potential between the two. The grooves are provided at least in that part of the insulator portion which is nearer to the free terminal and are separated from each other by ribs having flanks which make with a plane normal to the axis of the insulator an angle of about 10*.

United States Patent.

Beesch 51 Sept. 12, 1972 [541 HIGH VOLTAGE SPARKPLUG [63]Continuation-in-part of Ser. No. 20,275, March 17, 1970, abandoned,

Stuttgart,

[30] Foreign Application Priority Data March 18, 1969 Germany ..P 19 13582.1

[52] US. Cl. ..313/13l, 313/118, 313/137 [51] Int. Cl. ..H0lt 13/20 [58]Field of Search ..3l3/118, 130, 131,137, 325;

' Primary Examiner-Roy Lake Assistant Examiner-Darwin R. l-lostetterAttomey--Michael S. Striker [57] ABSTRACT A high-voltage sparkplug hasan electrically conductive housing from one end of which agroundelectrode projects. An elongated center electrode extends through thehousing and has a first end portion projecting from the one end anddefining a spark gap with the ground electrode and a second end portionprojecting from the opposite end of the housing and having a freeterminal. An electrical insulator insulates the center electrode fromthe housing and includes-an elongated insulator portion which surroundsthe second end portion of the center electrode intermediate the housingand the terminal and is provided in its outer circumferential surfacewith a plurality of axially spaced grooves which serve to retard currentleakage between the terminal and the housing by increasing the sparkoverpotential between the two. The grooves are provided at least in thatpart of the insulator portion which is nearer to the free terminal andare separated from each other by ribs having flanks which make with aplane normal to the axis of the insulator an angle of about 10.

[56] References Cited UNITED STATES PATENTS 2,723,364 11/1955 Ciprianiet a1. ..315/58 FOREIGN PATENTS 0R APPLICATIONS 893,137 4/1962 GreatBritain ..174/212 1 E E R l PATENTEDsmzmn 3.691.418

SHEET 2 OF 2 Fig. 3 5 #299 IN VENTOR 07m BENCH BY wwf fa/M ATTORNEY HIGHVOLTAGE SPARKPLUG CROSS-REFERENCES TO RELATED APPLICATIONS The presentapplication is a continuation-in-part of 5 my previous application, Ser.NO. 20,275, filed on Mar. 17, 1970, now abandoned under the title HIGH-VOLTAGE SPARKPLUG.

BACKGROUND OF THE INVENTION The present invention relates generally tospark plugs, and more particularly to high-voltage sparkplugs. It isknown to construct sparkplugs in the outer circumferential surface ofthat portion of their insulator which is located exteriorly of thesparkplug housing, with circumferential grooves which increase thecurrent leakage path between the center electrode and the housing whichis connected to ground, to thereby reduce spark-over. The conventionalsparkplugs provided with such grooves are employed under conditionsrequiring a medium potential, under which circumstances the increas ofthe current-leakage path afforded by these grooves-which usually are oftriangular or near-triangular cross-section--is entirely adequate.

However, increasing developments and refinements in internal combustionengines have brought and are still bringing with them additionalproblems. Thus, the requirements for increasing the compression ofcombustion engines, providing pollution control measures and analogousrequirements necessitate an increasingly high voltage potential which,in turn, leads to increasing spark-over potential. It has been foundthat under these circumstances the length of current leakage pathsobtainable in the known sparkplugs-always keeping in mind that it isdifficult if not impossible to increase the height or length of thesparkplugs because of other requirements which dictate this dimension-isinadequate without changing the length or height, so that these knownsparkplugs no longer are capable of preventing spark-over between theterminal of the center electrode at which the latter is connected with avoltage supply, and the housing.

Reference may be has to US. Pat. No. 2,723,364 to Cipriani et al. whichdiscloses an insulator with a pair of grooves remote from the exposedterminal of the center electrode and serving primarily to prolong theuseful life of a carbonaceous resistor in an axial bore of theinsulator. The grooves are flanked by surfaces which are stronglyinclined with reference to a plane normal to the axis of the insulator.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a high-voltage sparkplug for use in internal combustion engineswhich is particularly suited to prevent current leakage between thehousing or shell of the sparkplug and the exposed part of the centerelectrode.

A further object of the invention is to provide a sparkplug wherein thespark-over potential is substantially increased over the value know fromand achievable with prior-art sparkplugs.

One feature of the invention resides in the provision of a high-voltagesparkplug for use in internal combustion engines which comprises aconductive housing or shell having opposite ends and a ground electrodeprovided at one of these ends. An elongated center electrode extendsthrough the housing and has a first end portion projecting from the oneend and defining a spark gap with the ground electrode. A second endportion of the elongated center electrode projects from the other end ofthe housing and has an exposed terminal remote from the latter. Anelectrical insulator insulates the center electrode from the housing andincludes an elongated insulator portion surrounding the second endportion intermediate the other end of the housing and the terminal. Atleast in that part of the insulator portion nearest the exposed terminalof the center electrode the insulator portion is provided with aplurality of circumferential ribs separated from each other by annularcurrent leakage-reducing grooves. These ribs have substantially radiallyextending flanks which make with respect to a plane that is normal tothe axis of the insulator an angle of substantially less than 20,preferably 5-l 5 and most preferably 10.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved sparkplug itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view, partlyin section, illustrating a sparkplug which is constructed in accordancewith the present invention;

FIG. 2 is a fragmentary sectional detail view, on an enlarged scale, ofthe electrical insulator of the sparkplug in FIG. 1; and

FIG. 3 is a view similar to that of FIG. 2 but further showing thedimensions of various parts of the insulator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawings indetail, and referring first to FIG. 1, the reference numeral 10 denotesa housing or shell which forms part of my novel sparkplug. This housing10 consists of steel. Secured to the housing 10 at one end thereof is aground electrode 11 which is conductively connected to the housing. Aninsulator 12 consisting of ceramic material capable of providing therequisite electrical insulation extends into the housing 10. Theinsulator 12 is gas-tightly mounted in the housing 10. Extending throughthe insulator is a high-voltage electrode 13 which is gastightly mountedin the insulator 12.

The free or terminal end of the electrode 13 is provided with anexterior thread (no reference numeral) which meshes with correspondinginterior threads provided on a cap nut 14 WHICH serves to connect to thecenter electrode 13 a voltage supply cable (not illustrated). The cablecan also be connected with the terminal end of the electrode 13 in someother manner, and it is not a part of this invention. The other end ofthe electrode 13 defines with ground electrode 11 a spark gap.

as shown in FIG. 3, and grooves 15 that are provided in the outercircumferential surface of the exposed portion-exposed with respect tothe confines of the housing 10-of the insulator 12.

As shown in FIG. 2, and in great detail in FIG. 3, four circumferentialribs 16 separated from each other by four circumferential grooves 15 areprovided in the upper portion of the circumferential surface ofinsulator 12 as viewed in the drawing. The flanks 16a and 16b of eachrib 16 make an angle of about 10 with a plane A-A which is normal to theaxis X-X of the insulator. As can be seen from the dimensions shown inFIG. 3 the average width, as considered in the direction of the axis X-Xof the insulator, each rib 16 is approximately the same as the averagewidth of each groove 15. Furthermore, each of the grooves 15 and ribs 16consist of two halves which are substantially symmetrical with referenceto a plane extending through the respective groove or rib in thedirection normal to the axis X-X of the insulator. The transitionbetween the flanks 16a and 16b and the peripheral surfaces 16c of theribs 16 and the surfaces 15a in the innermost regions of the grooves 15have been smoothed. These transitions are shown in FIG. 3 with radii ofcurvature of 0.3 mm and 0.4 mm respectively. It will be noted that theinsulator 12 is slightly tapered. At its upper end ithas a diameter of11.8 mm which increases to a diameter of 12.2 mm at the lowest rib. Thediameter of the insulator at the uppermost groove is 10.0 mm whichincreases to a diameter of 10.3 mm at the lowest groove.

It has been determined that for the purpose of preventing currentleakage best results would be achieved if the ribs would have flankswhich are paral lel to the plane A-A. However, for convenience inmanufacture, a small angle substantially less than 20 has been foundsatisfactory to achieve the objects of this invention. For example, suchangle can be between and 15.

Due to such selection of the angle, the grooves are of a substantiallytrapezoidal cross-section. It is these grooves, and more particularlytheir cross-sectional configuration, which retards current leakagebetween the terminal 13 and the housing by increasing the spark-overpotential between the two. The rounded surfaces that make up thetransition between the peripheral surfaces of the ribs, the flanks, andthe innermost region of the grooves prevent potential peaks anddischarges from these junctures as could take place if the junctureswere sharp rather than rounded.

It has been found that with a sparkplug constructed in accordance withthe present invention and without increasing the number of grooves it ispossible to achieve an increase of approximately percent in thespark-over potential between the center electrode 13 and the housing 10.The spark-over potential can be increased in the sparkplug according tothe present invention, for example, from 27,000 volts attainable with aconventional sparkplug to 31,000 volts. The grooves are (but need notbe) of substantially trapezoidal crosssection and constitute aleakage-barrier which prevents spark-over between the center electrodeand the sparkplug housing in the potential range in question.

It is emphasized that by increasing the number of grooves 15 thespark-over potential can be further increased, that is the spark-overwill be further retarded.

To my knowledge no sparkplugs were available prior to the inventionwhich were capable of meeting the increased requirements made of themwith respect to spark-over potential, thus making it in turn impossibleto meet the requirements which are now being made by engine designers inview of anti-polution measures, higher compression ratios, and the like.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. A high-voltage sparkplug for use in internal combustion engines,comprising an electrically conductive housing having opposite ends; aground electrode provided at one of said ends; an elongated centerelectrode extending through said housing and having a first end portionprojecting from said one end and defining with said ground electrode aspark gap, and a second end portion projecting from the other of saidends and having a terminal remote from the latter; and an electricalinsulator insulating said center electrode from said housing andincluding and elongated insulator portion having an outer surface andsurrounding said second end portion intermediate said other end and saidterminal, said insulator portion having a plurality of circumferentialribs separated from each other by annular current-leakage retardinggrooves and said ribs having substantially radially extending flanksmaking with a plane which is normal to the-axis of said insulator anangle of substantially less than 20.

2. A sparkplug as defined in claim 1, wherein said angle is between 5and 15.

3. A sparkplug as defined in claim 1, wherein said angle isapproximately 10.

4. A sparkplug as defined in claim I, wherein said elongated insulatorportion includes a first part nearer to and a second part remote fromsaid terminal, said ribs and said grooves being provided at least insaid first part of said insulator portion.

5. A sparkplug as defined in claim 1, wherein the average width of saidgrooves, as considered in the direction of said axis, at leastapproximates the average width of said ribs.

6. A sparkplug as defined in claim 1, wherein said insulator portionfurther comprises annular faces disposed in said grooves between saidribs, there being a smooth transition between each of said annular facesand the adjoining flanks.

7. A sparkplug as defined in claim 1, wherein each of said ribs has anannular peripheral surface, there being a smooth transition between eachsuch peripheral surface and the flanks of the respective rib.

8. A sparkplug as defined in claim 1, wherein said insulator consists ofceramic material, and wherein said ribs define four grooves.

9. A sparkplug as defined in claim 1, wherein the flanks of each of saidribs are substantially mirror symmetrical with reference to a planehalving the respective rib and normal to said axis.

1. A high-voltage sparkplug for use in internal combustion engines,comprising an electrically conductive housing having opposite ends; aground electrode provided at one of said ends; an elongated centerelectrode extending through said housing and having a first end portionprojecting from said one end and defining with said ground electrode aspark gap, and a second end portion projecting from the other of saidends and having a terminal remote from the latter; and an electricalinsulator insulating said center electrode from said housing andincluding and elongated insulator portion having an outer surface andsurrounding said second end portion intermediate said other end and saidterminal, said insulator portion having a plurality of circumferentialribs separated from each other by annular current-leakage retardinggrooves and said ribs having substantially radially extending flanksmaking with a plane which is normal to the axis of said insulator anangle of substantially less than 20*.
 2. A sparkplug as defined in claim1, wherein said angle is between 5* and 15*.
 3. A sparkplug as definedin claim 1, wherein said angle is approximately 10*.
 4. A sparkplug asdefined in claim 1, wherein said elongated insulator portion includes afirst part nearer to and a second part remote from said terminal, saidribs and said grooves being provided at least in said first part of saidinsulator portion.
 5. A sparkplug as defined in claim 1, wherein theaverage width of said grooves, as considered in the direction of saidaxis, at least approximates the average width of said ribs.
 6. Asparkplug as defined in claim 1, wherein said insulator portion furthercomprises annular faces disposed in said grooves between said ribs,there being a smooth transition between each of said annular faces andthe adjoining flanks.
 7. A sparkplug as defined in claim 1, wherein eachof said ribs has an annular peripheral surface, there being a smoothtransition between each such peripheral surface and the flanks of therespective rib.
 8. A sparkplug as defined in claim 1, wherein saidinsulator consists of ceramic material, and wherein said ribs definefour grooves.
 9. A sparkplug as defined in claim 1, wherein the flanksof each of said ribs are substantially mirror symmetrical with referenceto a plane halving the respective rib and normal to said axis.